The lead connections from semiconductor elements formed on semiconductor crystals are extremely thin and thus the connecting wires must meet rigorous requirements to permit them to be securely connected or bonded to the semiconductor element or terminal track on a crystal, and yet be mechanically strong and reliable to insure electrical as well as mechanical integrity of the connection.
Connecting wires of the type to which the present invention relates have diameters in the order of between about 0.01 to 0.06 mm. Usually, terminal connecting wires were made of gold, aluminum, or aluminum alloys such as AlSi1, AlCu4 or AlMg1. The wires are usually bonded to the semiconductor by ultrasonic welding or thermo compression welding, or by a combination of both welding processes, known as thermosonic welding. Known aluminum and aluminum alloy ultra-thin wires are well suited for ultrasonic welding, but there is a tendency to form fissures in the region of the wire between the bonding point and the so called loop due to metal fatigue.
Known aluminum and aluminum alloy ultra-thin wires can be used as bonding wires in the thermo compression or thermosonic welding methods according to the process of the nail head or button termination only in a limited way. Other than ultra-thin gold wires, the region of the aluminum wires which is close to the bonding point tends to crack when making the loop formation.